# Copyright 2020 The Cirq Developers
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

from __future__ import annotations

import numpy as np

from cirq.experiments import purity_from_probabilities


def test_purity_from_probabilities() -> None:
    probabilities = np.random.uniform(0, 1, size=4)
    probabilities /= np.sum(probabilities)
    purity = purity_from_probabilities(4, probabilities)
    np.testing.assert_allclose(purity, np.var(probabilities) * 80 / 3)
